6 distinct types of resorption associated with tooth impaction

Published: February 2015

Bulletin #41 – February 2015

6 distinct types of resorption associated with tooth impaction

When we talk, read or write about patients with impacted teeth, it
is unavoidable not to mention the possibility of resorption and, when we do so,
we generally refer to resorption of roots. However, it is perhaps more relevant
in the context of tooth impaction to refer to resorption of dentine, because
there are situations in which resorption affects the dentine within the crown of
the tooth. Furthermore, resorption of enamel occurs in relatively rare
instances and this, too, is relevant to the present discussion.This month’s bulletin is dedicated to a
discussion of 6 different and distinct resorption entities that are seen in patients
who suffer from tooth impaction in its many incarnations.

1.Root resorption as a by-product of
routine orthodontic treatment.

Root
resorption occurs during orthodontic treatment with great frequency although
its extent and its implications are rarely of any serious concern. To see a
patient in whom the process has been extremely vigorous and in whom much of the
roots of bracketed teeth have been severely resorbed is, for most of us, a
once-in-a-professional-lifetime nightmare encounter. In general, when
resorption is noted it is typically characterized by a rounding off of the
apices of a number of teeth in the same dentition, rather than a single tooth.
In terms of dental health and prognosis of the teeth concerned, it has no
clinical significance. Etiology may involve patient-related factors, which
include genetics, systemic factors, asthma and
allergies, chronic alcoholism, the severity of malocclusion, tooth-root
morphology, a previous history of root resorption, alveolar bone density, root
proximity to cortical bone, endodontic treatment, and patient age and sex.
Orthodontic-related risk factors include treatment duration, magnitude of applied
force, direction of tooth movement, amount of apical displacement, and method
of force application.1-11

The teeth remain vital and the resorption process arrests when the
orthodontic forces are discontinued.

A very new study has indicated
that orthodontic treatment of impacted maxillary canines does not appear to
result in more resorption than does orthodontic treatment of malocclusions
without tooth impaction. However, the authors warn that, because of the
observational nature of the study, caution should be exercised in
interpretation of the results.12

2.Resorption of the root of the adjacent
tooth associated with the aberrant eruptive progress of an impacted canine

Resorption of the
root of the immediate neighboring tooth is a well-known phenomenon that occurs
more frequently than was once thought, because of the vast improvements that
are provided by the diagnostic imaging methods that are available today. In the
era that preceded computerized tomography (CT), plane film (2D) conventional radiography
was the sole means of diagnosing root resorption. Thus, an epidemiologic study
of its prevalence carried out in Sweden using plane film radiography13, 14
concluded that resorption occurred in 12% of the children with impacted
maxillary canines. However, the authors recognized that this was probably an
understatement of the problem. As they pointed out in their report, the
impacted canine usually overlaps incisor root on its labial or palatal aspect,
which are areas that cannot be portrayed or examined on plane films. This means
that unless or until a resorption lesion of incisor root actually altered the
shape of the root in the interproximal area, it is impossible to diagnose its
presence.

This study was
repeated by the same research group a few years later, when they had access to
the then new spiral CT machines15. Given this vastly superior
diagnostic modality with its inclusion of a third dimension capability, the
bucco-lingual surface of the two adjacent teeth became radiographically
accessible. From the results of this study, the researchers discovered the
ability to diagnose incisor root resorption in almost half the cases of canine
impaction, many of which were in their early stages. A further study was
carried out by the group in Southern California using cone beam CT technology16
and their results indicated a prevalence of 67% identifiable resorption lesions
in a similar sample of impacted canine cases. With this level of vulnerability,
it stands to reason that patients with impacted canines should be screened for
resorption.

This leaves the orthodontist with a few questions to answer:

a.Is the condition progressive?

b.Can it be stopped?

c.Can an incisor with advanced root
resorption recover

d.Can the tooth subsequently be moved
orthodontically without further risk of resorption

Fig. 1a. A periapical view of 2 impacted maxillary
canines associated with almost total resorption of the roots of all four
incisors.

Fig. 1b. A series of cross-sectional (transaxial) cuts of
the left side central and lateral incisors shows the extreme degree of the
resorption in the same case.

This type of root
resorption is very rapid and aggressive (Fig. 1). The study showed that during
the period in which orthodontic treatment was initiated to level, align and to
open space for the canine, a further increase of 17% in the crown-root ratio of
the incisor was recorded i.e. the root was further shortened. It was also noted
that, once the aggressive canine was distanced from the immediate area, the
resorption rate dropped to an insignificant level. Accordingly, tackling the
canine as a first orthodontic/surgical priority is advised, even before any
attempt is made to move other teeth. Once the canine is distanced, the resorbed
incisors may be bracketed and moved orthodontically, with care exercised not to
exceed accepted force values - taking into account the fact that short rooted
teeth have a reduced root area. Even a resorbed incisor that initially
displayed a marked degree of mobility recovers its firmness. Radiologically,
the previous radiolucent area in the intervening resorption space between
canine crown and incisor root end becomes filled with normal trabecular bone,
the incisor acquires a lamina dura and subsequent orthodontic movement of the
tooth does not then cause further root resorption. The incisor teeth do not lose
their vitality, do not undergo unacceptable changes of color and do not need
periodontal splinting, although orthodontic retention must remain a
consideration.

The same Swedish group mentioned above
has performed research in other aspects of this area. In one of their studies,
they investigated possibly linkage of resorption with the size of the follicle
surrounding the crown of the canine.18 Their findings were that
reduced or virtual absence (in radiologic terms) of the follicle (i.e. actual
contact between the canine crown and the incisor root) was a common finding in
relation to resorption. They further found that an enlarged follicle had no
apparent association with the resorption, which is contrary to that seen in a
subsequent study by the same group19 and to the experience that I
have had in these cases.

Invasive cervical root resorption is a pathologic condition of the
impacted tooth itself, rather than of its immediate neighbor. As its name implies,
it is generally found in the area of the neck of the tooth close to the CEJ,
although similar lesions may occasionally be found elsewhere on the surface of
the roots of teeth (http://dr-adrianbecker.com/page.php?pageId=281&nlid=115 Bulletin #40 January 2015). It is caused
by a non-inflammatory infiltration of clastic cells that derive from the PDL
and gain direct access to the root surface through gaps in the cementum
layer.It appears to have an association
with previous trauma, presumably because it causes loss of cementum at a
specific point on the root’s surface, close to the CEJ. There is loss of PDL
integrity at this point, which permits the clastic cells to come into direct
contact with the root surface. The site at which the cells begin their work of
destruction becomes a point of entry and the resorptive lesion then mushrooms
out into the body of the root (Fig. 2).

Fig. 2a. An axial cut across the roots of maxillary teeth
shows an advanced ICRR lesion resorbing the disto-lingual aspect of the root of
the canine (arrow). It is worth noting that the pulp chamber is depicted as a
circle, because the lesion does not cause resorption of the predentine layer
adjacent to the pulp, probably due to its high organic content.

Fig. 2b. Two successive cross-sectional (transaxial) cuts
show the small point of entry of the lesion (arrow). The radiolucent lesion can
be seen to proliferate apically and coronally.The thin vertical wall of the predentine can be seen in the left cut,
separating the lesion from the pulp.

Fig. 2c. A 3-D video clip of a similar lesion in a
maxillary left second premolar, showing its exact location and extent in terms
of depth, width and height within the tooth.Video preparation by Mr. Amnon Leitner of Panorama Nahariyah, Israel.

Histologically, resorptive lacunae are seen on prepared microscope
slides and one may also see an adjacent area of bony deposition in the depth of
the ICRR lesion.20, 21 Whether it is due to the break in the
integrity of the PDL or the deposition of bone in the lesion, the tooth will
not erupt and neither will it respond to eruption mechanics. Typically, after a
lengthy period of attempted forced eruption in such cases, the patient is often
referred back to the oral surgeon with the request that the tooth be surgically
luxated – on the misguided assumption that the tooth has become ankylosed. When
the surgeon grasps the tooth in the forceps it is discovered that the tooth is
mobile!

As reported in the #20 and #39 bulletins in
this series from March 2013 (http://www.dr-adrianbecker.com/page.php?pageId=281&nlid=114 and December 2014 (http://www.dr-adrianbecker.com/page.php?pageId=281&nlid=54respectively, the features of ICRR are
that the lesion is fairly rapidly progressive, proceeding in all direction in
the root. It reaches the predentine layer surrounding the pulp and is arrested
by its relatively high organic content. It therefore encircles the pulp without
actually breaking through and it advances both coronally and apically to resorb
the dentine structure in all directions. Since it is not an inflammatory
process, it is entirely asymptomatic, does not stimulate the production of
secondary dentine and is often discovered when the damage is well beyond
repair. If treatment is to be offered to overcome the problem, the lesion must
be exposed surgically and then sealed off from its contact with the PDL. If the
lesion is excavated with the aim of eliminating all the softened dentine mush,
vital exposure of the pulp is both inevitable and utterly superfluous. The nutritive
supply line of the resorptive process is from the PDL and not from the pulp.
This is not caries and should not be treated as such. Therefore, superficial
removal of the affected dentine is indicated simply to provide a shallow cavity
whose outer wall is free of the resorption mush. If this carefully and
conservatively prepared cavity is then restored with glass ionomer or other
restorative material, the clastic elements will have become sequestrated from their
nutritive source and will be arrested within the sealed-off cavity. The tooth
will then respond to eruptive forces, both natural and applied and the
impaction may be resolved.21 Later definitive treatment of the
sealed-in mush may be undertaken many months after the restored margins of root
surface will have been raised supragingivally and optimal conditions of access
for endodontic and restorative treatment will have been achieved.

The force of reaction to extrusion of an impacted tooth is,
according to Newton’s Third Law of Motion, equal and opposite to the force
delivered to extrude the impacted tooth. In other words there is a force of
intrusion applied to the adjacent anchor teeth, which may result in actual
intrusion of these teeth, particularly if the treatment lasts for many months.
When an orthodontist is faced with impacted teeth which do not respond to the
extrusive forces, perhaps as the result of inappropriate directional force,
ankylosis or ICRR, the practitioner will be reluctant to give up. Typically,
he/she will increase the force and see the patient more frequently to renew its
application for a longer period, instead. In many instances, a year or more of
fruitless traction may be applied before the decision is made that ankylosis or
invasive cervical resorption is present. A new radiograph taken at this late
stage will witness a definite shortening of the roots of the adjacent anchor
teeth in many of these cases (Fig. 3).

Fig. 3a, b. Panoramic and periapical views before (left
side) and after (right side) treatment for ankylosis of the first molar. The
treatment involved fruitless orthodontic traction initially, followed by
successful luxation of the molar and the application of heavy orthopedic
forces. A comparison of the before and after views will reveal the root
shortening and rounding of the apices of the adjacent premolars.

This type of resorption has similar characteristics to the root
resorption that occurs more generally in routine cases, with the exception that
it is observable almost entirely on just one or two of the adjacent anchor
teeth to a significant degree, but without adverse effects on the other teeth
in the dentition. Discontinuing the forces will arrest the process.

5.Pre-eruption
intra-coronal resorption (PEIR).

This phenomenon is also known as penetrating crown resorption of an
unerupted tooth, pre-eruption caries, occult caries, hidden caries, pre-eruptive
dentine translucencies and several other names. However, it is not dental
caries and has been discussed at length in bulletin #24 of July 2013 in this
series, at http://dr-adrianbecker.com/page.php?pageId=281&nlid=59 .

Fig. 4a. A series of cross-sectional (transaxial) views
through the impacted mandibular canine. The arrows point to a lesion of
pre-eruptive intra-coronal resorption (PEIR) with its origin in the cusp tip. Courtesy of Dr. Adam Renart.

Fig. 4b. A PEIR lesion has devoured most of the crown of
the unerupted maxillary canine.

It would appear to be closely related to invasive cervical root
resorption and its progress and histopathology are probably identical. The
obvious difference is that ICRR enters through gaps in the cementum layer
covering the dentine of the root of the tooth, while PEIR enters through the
crown of the unerupted tooth, through a developmental gap in the enamel, often
found in an occlusal pit or fissure or cusp tip (Fig. 4a). However, since it
too is asymptomatic, it may progress to destroy most of the crown of the tooth,
eventually including the enamel (Fig. 4b). It differs from ICRR because PEIR is
arrested when the tooth erupts into the oral environment. Once the tooth has
erupted, it loses its nutritive supply line from the follicle and the clastic
cells, that had been hitherto burrowing into the dentine of the crown and
undermining the enamel, will die. However, the tooth may later become
secondarily infected with true dental caries in the depths of the now open
occlusal crevices. This is probably the origin of such misnomers as hidden or
occult caries.

Unlike ICRR, which causes the tooth to resist eruption, unerupted
teeth with an early PEIR lesion may erupt presumably because the dental
follicle is complete and can play its part in fusing with the overlying oral
epithelium to open an eruption canal. Anecdotally, however, I have noticed that
in the presence of an extensive PEIR lesion is seen, the tooth does not usually
erupt.

Treatment entails exposing the affected crown of the tooth to the
oral environment, thereby causing the active clastic cells to die. Since the
resorption mush within the crown is not caries, excavating it has little
purpose. On the contrary, any instrumentation aimed at eliminating it will
almost certainly cause pulp exposure and necessitate immediate root canal
therapy, in circumstances where access is very poor. Once exposed, a simple
temporary dressing placed to seal off the lesion.

With advancing age, it becomes more problematic to attempt to
resolve the impaction of teeth by orthodontic means, in terms of both the
duration of treatment and its failure rate.22Why this should be is
not clear but, in a good proportion of the cases, radiographs will reveal
collapse of the dental follicle around the crown of the tooth. This permits
direct contact between the enamel of the unerupted tooth and the surrounding
tissues. At the time of exposure surgery, the surgeon will note soft tissue and
bony adhesions to the enamel. In the more advanced cases, the enamel surface
becomes pitted due to actual surface resorption of the enamel. In these cases,
unless complete dissection of the tissues around the fully exposed crown of the
tooth is performed, orthodontic traction of the tooth will fail to move the
tooth. Even with full exposure, the chances of recurrence may be high,
notwithstanding the placement of an isolating surgical pack. The tooth is in
effect ankylosed.

Fig. 5. A 66 year old female patient with a spaced
dentition and a peg-shaped lateral incisor. An impacted maxillary canine was a
chance radiographic finding in a routine dental examination. Note the lack of
clarity of its outline, the loss of much of the radiopacity of its crown and
the absence of most of its dental follicle. The tooth has suffered much
replacement resorption of much of the enamel of its crown and is ankylosed.

This condition should be possible to diagnose from a simple
periapical film (Fig. 5). It will show a very narrow space between follicle and
tooth, which may be missing in certain areas. It may also show a blurring of
the usually distinct and clear outline of the crown of the tooth and a degree
of loss of contrast of its enamel layer. This will be less obvious on a
panoramic scan.

11.DarendelilerMA, and others: a 24 part series of
research articles on root resorption that appeared in the American Journal of
Orthodontics and Dentofacial Orthopedics under the general title Physical properties of root cementumAm J Orthod Dentofacial Orthop. 2001;120:198-208 to Am J Orthod Dentofacial Orthop. 2014;145:617-25 incl.

12.EvangeliaLempesi,NikolaosPandis,Padhraig
S.Fleming,MariaMavragani A comparison of apical root resorption
after orthodontic treatment with surgical exposure and traction of maxillary
impacted canines versus that without impactions.Eur J Orthod.2014;36:690-7